VERNIER CALLIPER
Q.1: What is vernier calipers?
Ans. It is simple instrument by which length of an object can be measured accurately up to one-tenth of a millimeter or one-hundredth of a centimeter.
Q.2: What is the use of Vernier Scale?
Ans. To increase the accuracy of the main scale.
Q.3: What is least count (L.C.)?
Ans. The minimum measurement that can be taken by an instrument.
Q.4: What is the least count of?
meter scale (b) Stop Watch (c) Vernier Calliper
Ans. The least count of:
meter scale = 0.1 cm or 1 mm.
stop watch = 0.01 sec or 1/100 sec. or according to stop watch.
vernier scale = 0.002 mm or 0.01 mm according to Vernier calliper
Q.5: What are units of vernier scale?
Ans. Vernier has not units of its own.
Q.6: What is the difference in the measurement of one smaller division on the main scale (M.S.) and that of vernier scale (V.S.)
Ans. (1 smallest Div. on M.S.) – (1 smallest Div. on V.S) = 0.1 – 0.09 = 0.01 cm = Least count.
Q.7: How the L.C. of a vernier is determined?
Ans. By using the relation:
L.C. = (Smallest division on Main Scale ) / (Total number of divisions on Vernier Scale)
Q.8: Will the accuracy of a vernier will increase or decrease if 20 divisions are made in the same length?
Ans. The accuracy will increase since the L.C. will decrease i.e. Accuracy α = 1 / Least count
Q.9: Which one is smaller M.S. div. or V.S. div.?
Ans. V.S. division.
Q.10: What are the functions of (a) Sliding strip (b) Upper jaws
Ans. (a) For measuring depth. (b) For measuring the inner diameter.
Q.11: What is meant by zero error (Z.E.)?
Ans. The error which arises when zeros of M.S. and V.S. do not coincide upon joining the two jaws.
Q.12: When Z.E. is positive?
Ans. The Z.E. is positive when the zero of V.S. is to the right of the zero of M.S.
Q.13: How we find the corrected reading?
Ans. Corrected reading = Meaning reading – ( + Z.E.)
Q.14: Do you know any use of vernier scale?
Ans. It is used in spectrometer, barometer, traveling microscope, etc.
Q.15: What are significant figures?
Ans. Numbers 0, 1, 2, 3, ……. are called significant figures when they occur. The zero is not a significant figure if it is at the extreme left or extreme right of a number, e.g. 1.02 has three significant figures, but 1.20 has two significant figures.
Q.16: What is meant by degree of accuracy?
Ans. It is the measurement estimated by the number of significant figures in the result.
Q.17: Why is the vernier calipers so called?
Ans. A French mathematician named Pierre Vernier invented it and it is named after him.
Q.18: How does temperature affect the length of a cylinder?
Ans. The length of a cylinder increases with the increase of temperature and decreases with the
decrease of temperature.
Q.19: What is the unit of volume?
Ans. In MKS system, the unit of volume is m3. In CGS system, the unit of volume is cm3. In FPS
system, the unit of volume is ft3.
MICROMETER SCREWGAUGE
Q.1: What is a screw?
Ans. Screw is a simple machine related to inclined plane.
Q.2: What is meant by “gauge”?
Ans. The gauge means device or instrument.
Q.3: Name two main parts of a screw-gauge?
Ans. (a) A nut (b) A bolt or screw
Q.4: What is meant by pitch of a screw?
Ans. Pitch is the distance between two nearest (consecutive or successive) threads along the axis of screw.
Q.5: How is the pitch found?
Ans. By dividing the distance covered by the screw in a known number of rotations by the total number of relations.
Q.6: What is the least count (L.C.) of the screw gauge?
Ans. L.C. of screw gauge = 0.001 cm.
Q.7: How the L.C. of a screw gauge is found?
Ans. By using the relation: L.C. = (Pitch of the screw / No. of circular scale divisions)
Q.8: What is meant by zero error of a screw-gauge?
Ans. The error which arises when the zero of circular scale does not coincide with the zero of the main scale upon joining the two studs.
Q.9: When the zero-error is positive?
Ans. If the zero of the circular scale lies above the reference line, provided that the fixed and movable studs are in contact.
Q.10: What is the degree of accuracy of the screw gauge?
Ans. Degree of accuracy = L.C. or Reading power = 0.001 cm
Q.11: What is mechanical advantage of a screw gauge?
Ans. Like a screw jack mechanical advantage of a screw gauge is 2π r/h; where ‘r’ is the radius of cylinder of the screw and ‘h’ is the pitch.
Q.12: What is meant by range of the screw gauge?
Ans. The maximum length of the main scale.
Q.13: What is formula for area of cross section of wire?
Ans. Area of circle = 2 π r
Q.14: What is back lash error?
Ans. Within a nut there is a little space for the play of screw. Due to continuous use this space increases. Thus when the screw is turned in one direction the stud moves as usual. However, when the screw is rotated in the opposite direction, the stud does not move for a while. This error is called Back lash error. In short “Back lash error is the error introduced on reversing the direction of rotation”.
Q.15: How back lash error is avoided?
Ans. By turning the screw in one direction only.
Q.16: What are “precision instrument”?
Ans. The instrument that can measure up to a fraction of a mm, e.g., vernier caliper, screw gauge and spherometer.
Q.17: What is Pi (π)?
Ans. Ratio between the circumference of a circle to its diameter. π = ( Length of Circumference / diameter )
Q.18: Does the diameter of the screw depend on temperature?
Ans. Yes it does. Diameter increases with the increase of temperature and decreases with the decrease of temperature.
SPHEROMETER
Q.1: Why the instrument is given the name “spherometer”?
Ans. Because it is used to determine the radius of curvature of a spherical surface.
Q.2: What is the pitch of a spherometer?
Ans. The distance covered by the circular disc in one complete rotation along the main scale. Mostly pitch of spherometer = 1 mm = 0.1 cm.
Q.3: How do you find the least count of spherometer?
Ans. L.C. of spherometer = (Pitch of screw / No. of divisions an circular scale) = (0.1 cm / 100) = 0.001 cm.
Q.4: What is meant by ‘radius of curvature’ of a surface?
Ans. The radius of that sphere from which the surface is cut.
Q.5: What is the radius of curvature of plane surface?
Ans. Infinite.
Q.6: Is paper insertion method for testing the touching position of the screw is correct?
Ans. No, because the thickness of ordinary paper (0.01 cm) is greater than the L.C.
Q.7: Is there any zero error in a spherometer?
Ans. Spherometer may have a zero error. Z.E. in spherometer = reading on the plane glass sheet
Q.8: When the zero error (Z.E.) is positive and when negative?
Ans. Positive: If the edge of the circular disc is at zero of main scale and the zero of the circular scale is ahead of the edge of main scale. If it is behind the edge of main scale, the Z.E. is negative.
Q.9: Can you measure the radius of curvature of wrist-watch glass by using a spherometer?
Ans. No, because the wrist-watch glass is small and all the legs of the spherometer cannot rest on it.
Q.10: What will be the effect of:
(a) changing the pitch or
(b) changing the number of circular divisions upon accuracy or least count.
Ans. (a) If we decrease the pitch the L.C. will decrease and hence the accuracy increases.
(b) If we increase the No. of circular divisions, the accuracy increases since the L.C. decreases.
Q.11: What are the other uses of spherometer?
Ans. (a) In finding a small increase in length during finding the coefficient of linear expansion.
(b) In finding the small change in length due to the change in the weight suspended during the
determination of young’s modules.
Q.12: Why main scale is marked on both sides of zero?
Ans. To measure both height and depth.
SIMPLE PENDULUM
Q.1: Define simple pendulum.
Ans. An ideal simple pendulum is defined as ‘single isolated particle suspended by a weightless,
flexible and inextensible string with a friction-less support’.
Q.2: Why the word ‘SIMPLE’ is used before the pendulum?
Ans. Because the pendulums used in the wall clocks are ‘COMPOUND PENDULUMS’, in which a metallic rod is used in place of the thread.
Q.3: Define ‘g’?
Ans. Acceleration due to gravity.
Q.4: What is the difference between ‘g’ and ‘G’?
Ans. The value of G (gravitational constant) remains constant throughout the universe, whereas the value of ‘g’ decreases with the increase in the height.
Q.5: What is the value of ‘g’ at the C.G. of the earth?
Ans. Zero.
Q.6: How the value of ‘g’ changes as we move from the surface towards the C.G. of the earth?
Ans. As a rule it should decrease gradually but due to variable density of the earth, it increases up to a small depth and then decreases.
Q.7: Where the ‘g’ is greater, at equator or poles?
Ans. At the poles (where the earth is slightly compressed).
Q.8: Where ‘g’ will be smaller, at Karachi or at Muree?
Ans. At Muree (7000 ft. above sea level).
Q.9: What is the value of ‘g’ at sea level?
Ans. g = 9.781 m/s2 at equator.
g = 9.832 m/s2 at poles.
Q.10: Why the amplitude of the pendulum is kept small (2cm or about 5 cm)?
Ans. If the amplitude is large the motion of the simple pendulum will not be simple harmonic. If θ will not be small Sinθ ≠ θ and T ≠ 2 √L/g.
Q.11: Define simple harmonic motion (S.H.M).
Ans. The motion of the vibrating body is S.H.M. when
(a) The magnitude of its acceleration is directly proportional to the displacement x from the mean position.
(b) The direction of acceleration is always towards the mean position (that is opposite to x) mathematically: a α – x
Q.12: Define vibratory system?
Ans. Back and forth or to and from motion between two fixed positions.
Q.13: Define the following terms: (a) amplitude (xo) (b) oscillation or vibration (c) frequency (f) (d) time period (T)
Ans. (a) Amplitude: the maximum displacement from the mean (equilibrium) position.
(b) Oscillation: the motion from one extreme position to the other and then back to the original one.
(c) Frequency: number of vibrations per second.
(d) time period: time taken for one vibration.
Q.14: What is the relation between frequency and time period?
Ans. f = (1 / T) or T = (1/F)
Q.15: What are the units of frequency?
Ans. Vibrations / sec, cycles / sec (c.p.s.) or Hertz.
Q.16: What is the frequency of a second pendulum?
Ans. 0.5 Hz or (1 / 2) Hz, because f = ( 1 / T ) = (1 / 2) ( T = 2 s for a second’s pendulum)
Q.17: Prove that g = 4 π2 (L / T2)
Ans. For a simple pendulum time period is given by:
T = 2 π √L/g
T2 = 4 π2 L/g
i.e. g = 4 π2 L/T2
Where L = length of the simple pendulum.
Q.18: Let the time period of a simple pendulum is 4s at the place where g = 900 cm/s2. What will be the time period at the place where g = 100 cm/s2.
Ans. 12 s.
EXPLANATION: g = 4 π2 (L/T2) => T2 α ( 1 / G) when L remain constant. Therefore, when g decreases by 9 times, the ‘T’ increases by 3 times.
Q.19: Time period will increase or decrease if we use a heavier bob.
Ans. There will be no change in the time period. EXPLANATION: The relation T = 2 √L/g shows that there is no effect of mass on the
time period.
Q.20: Can you replace the thread by a metallic wire?
Ans. No, because the wire is not flexible. EXPLANATION: By definition of simple pendulum, the string must be perfectly flexible. The
thread is flexible but a metallic wire is not. That is why the wire can be used in place of thread.
Q.21: What is restoring force?
Ans. The force which tends to bring a vibrating body towards the mean position.
Q.22: What is restoring force (net force) acting on the bob?
Ans. If the air friction is neglected, restoring force on the bob = mg Sin θ.
Q.23: What is net force on the bob, at equilibrium (mean) position?
Ans. Zero, since at mean position the weight of the bob is perfectly balanced by the tension (T) in the string.
Q.24: Define equilibrium.
Ans. A body is said to be in equilibrium when its linear and angular accelerations are zero or when F = 0 &
EXPLANATION: when a body is
(a) at rest or
(b) moving with uniform linear velocity its linear acceleration is zero.
(c) not rotating at all or
(d) rotating at a constant rate it is in equilibrium.
Q.25: Can you replace the thread by a rubber band?
Ans. No, because it is not inextensible. By definition the string must be inextensible.
Q.26: Can we use a cricket ball in place of the bob?
Ans. No, by definition of simple pendulum the bob must be as small as possible.
Q.27: Why the pendulum stops after some time?
Ans. Its energy is lost as heat.
Q.28: How P.E. and K.E. of the pendulum interchange into each other during vibrations?
Ans. (a) In the form of P.E. at extreme positions.
(b) In the form of K.E. at mean position and
(c) In the form of P.E. and K.E. between mean and extreme positions.
Q.29: From where the length of the pendulum is measured?
Ans. From the centre of gravity of the bob to the point of suspension.
GLASS SLAB
Q.1: What do you mean by refractive index?
Ans. Refractive index of a medium determines the extent to which one medium is optically denser than the other medium for a particular of a light used.
Q.2: What is absolute refractive index?
Ans. When light passes from vacuum into another medium than the ratio of the since of angle of incidence to the sine of angle of refraction is called absolute refractive index.
Q.3: On what factors refractive index depends?
Ans. It depends:(a) Nature of medium (b) Wave length of incident light.
Q.4: What is the unit and the use of refractive index?
Ans. Being a ratio refractive index has no units and it is used to test the purity of a material because every pure material has a definite refractive index.
Q.5: Why does an object appear near through glass or water?
Ans. It is due to refraction of light.
Q.6: If an object is placed under the glass slab what type of its image is formed?
Ans. Virtual image is formed in the glass slab.
Q.7: What is meant by critical angle?
Ans. When refraction tales place from a denser to rare medium, the angle of incidence for which the corresponding angle of refraction is 90o is called critical angle.
Q.8: On what factors critical angle depends?
Ans. It depends upon the nature of material and the nature of the medium in which the material is placed. It also changes with the colour of light, greater for red light and smaller for violet light.
Q.9: Define total internal reflection?
Ans. When light strikes the surface of an optically rare medium to an angle of incidence greater than the critical angle, light instead of emerging into the rare medium is reflected back into the denser medium. This phenomenon is called total internal reflection.
Q.10: Under what conditions total internal reflection occur?
Ans. (a) The light must pass from a denser to rare medium.
(b) Angle of incidence in the denser medium must be greater than the critical angle for that
medium.
PRISM
Q.1: What is a prism?
Ans. A piece of transparent medium bounded by three rectangular and two triangular surfaces.
Q.2: Define deviation.
Ans. Total bending of a ray of light while crossing on optical medium.
Q.3: Define angle of deviation (D).
Ans. The angle between the incident ray and the emergent ray.
Q.4: What is the relation between the angle of incidence and the angle of deviation?
Ans. When the angle of incidence starts increasing from a smaller value, at first the angle of deviation decreases up to a certain limit (angle of minimum deviation) and then it increases.
Q.5: How does the angle of deviation vary with the wave length?
Ans. Shorter the wavelength, greater will be the angle of deviation.
Q.6: What is the relation between wavelength and energy?
Ans. Inverse proportion i.e. shorter the wavelength, greater is the energy of a colour.
Q.7: What is angle of prism in this experiment?
Ans. 60o.
Q.8: How angle of prism is related with the angle of deviation?
Ans. larger the angle of prism, larger is the angle of deviation.
Q.9: Give some examples of total internal reflection.
Ans. (a) Mirage (b) Glittering of precious stones (c) Shiny appearance of the water surface of swimming pools as seen from inside the water.
Q.10: When light enters into the prism is there any change in the frequency of wave length?
Ans. The wavelength decreases but the frequency does not change.
Q.11: What is the relation between the speed of light (C) frequency (υ) and wave length (λ)?
Ans. C = υ x λ
Q.12: What is unit of refractive index?
Ans. No units, because it is the ratio between two similar quantities.
Q.13: Which of the colours have maximum and minimum angle of deviations?
Ans. The deviation is greater in the violet colour and smallest is red.
Q.14: Why the danger signals are red?
Ans. Since the deviation in the red colour is minimum, therefore, they can be seen from the maximum distance.
Q.15: Define dispersion of light.
Ans. Separation of colours present in polychromatic light by a prism.
Q.16: Give any example of dispersion.
Ans. Rainbow in the sky due to droplets of water.
Q.17: What are totally reflecting prisms?
Ans. The prisms in which the angle of prism are 90o, 45o and 45o.
Q.18: What kind of glass is used for making prism?
Ans. Crown glass or optical glass.
Q.19: Why is PO cut equal to OM in this experiment?
Ans. Because the image is formed at the same distance behind as the object is in front of the reflecting face of the prism.
Q.20: What is meant by critical angle?
Ans. When refraction takes place from a denser to a rare medium, that angle of incidence for which the angle of refraction is 90o, is called the critical angle.
Q.21: What is totally reflecting prism?
Ans. It is a glass prism having angles of 45o, 45o, 90o. It deviates the path of light through 90o or180o without any loss in intensity.
Q.22: Why do the precious stones like diamond glitter?
Ans. These precious stones have large refractive indices and small critical angles which make the incoming light totally reflected a number of times without much loss in intensity and hence make their faces look bright.
LENS
Q.1: What is a lens?
Ans. A lens is a portion of a transparent medium bounded by two spherical surfaces or by one
spherical surface and a plane surface.
Q.2: How many principal foci are there for a lens?
Ans. Two, one on either side of the lens.
Q.3: What is the reference point for measuring p, q and f for a lens?
Ans. The optical centre of the lens.
Q.6: If the power of a convex lens is 0.1 diopter; what will be its focal length?
Ans. P = 1/f, so that, f = 1/p = 1/0.1 = 10m
Q.7: Which defect is present in lenses but not in mirrors?
Ans. Chromatic aberration.
Q.8: What are uses of lenses?
Ans. Combination of lenses are used in microscopes, telescopes, projectors, binoculars, cameras, etc.
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